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Why we age at different rates: Genetics vs environment

Aging, at least for now, is an inevitable process for us human beings. How we age though, and aging in good health begins before we even realize. Before we are born, our genetic inheritance is laid down, yet can easily be influenced by the environment while we are even still in the womb.

On the biological level, ageing does in part come down to your genes. When hair starts to grey for example, or being prone to baldness will be a direct lineage from your father. However, exposure to a stressful environment or unhealthy habits may lead to premature greying regardless of your genetic background. Scientists believe that this phenomenon comes down to epigenetics. Epigenetics is the study of biological mechanisms which influence the way your genes are expressed, without affecting the underlying DNA sequence. Epigenetic events are highly complex and orchestrated to influence cellular decisions and fate, and are directly impacted by environmental factors.Contrary to initial hypotheses, recent research has revealed that decisions we make can influence not only our own epigenome, but our children's and even grandchildren after us. Perhaps the most well characterized epigenetic mark is DNA methylation. Methylation patterns exist in every cell in the body and are critical for proper control of gene expression. DNA methylation patterns are often abnormal in disease, and are prone to environmental influences. For example, it is well accepted that smoking during pregnancy is harmful to the developing fetus. Studies have highlighted that chemicals found in cigarette smoke directly alter DNA methylation patterns, which has numerous side effects, including low birth weight and developmental problems. Even more striking studies have emerged from controlled populations, indicating the environment your parents were exposed to, might have influenced you. For example, children of Holocaust survivors were found to have aberrant methylation patterns which predisposes them to stress disorders.

Cause or consequence?

What is not known, is whether epigenetic changes are the cause or consequence of genetics. It is clear that they go hand-in-hand and are implicated in ageing as well as many diseases, including cancer, a disease more prevalent among older populations and in more developed societies. These findings have led to a surge in the pharmaceutical industry to identify drugs which can block or even reverse epigenetic events, opening the possibility of treating age-related diseases and subsequently prolonging ageing.Since epigenetic events are due to environmental factors, is it possible to naturally slow down our ageing clock? It is well known that societies which have a healthy lifestyle, not only live longer, but have a good quality of life, and are less prone to disease. Being from a Mediterranean country as an example, where plant based diets, filled with fresh fruit and vegetables and healthy fats from olive oil and fish as well as a less stressful lifestyle is the norm. Scientific evidence shows that such plant-based diets may promote longevity through delayed telomere shortening. Telomeres are important structures which cap and protect the ends of our chromosomes from fraying and damage. One study on over 4500 individuals showed those who ate a more plant based diet had an increase in telomere growth while those having a more unhealthy diet had shorter telomeres and impaired growth.

The enzyme telomerase, co-discovered by 2009 Nobel Prize winner Dr. Elizabeth Blackburn, governs the growth of telomeres. Currently, Blackburn and her team are investigating the role stress has to play in telomere growth. Stress and depression seem to pose negative effects on telomere length and thus, aging. Interestingly, the team are leading trials in which mindfulness meditation is introduced to alleviate stress, protecting telomeres from shortening and thereby prolonging cellular aging.

Aging and your microbiome - correlation or causality

While us humans are a complex species, made up of around 100 billion diverse cells, we have evolved to coexist with 10 times that amount of bacteria, mainly found on our skin or in our gastrointestinal tract. Recent advances in high-throughput sequencing have allowed us to appreciate our complex relationship with bacteria (microbiome). The Human Microbiome Project http://hmpdacc.org/ led by the NIH is an online repository for research in this area, and aims to characterize the human microbiome and its role in human health and disease.

This is a rapidly advancing research field, and there have already been many associations made linking our health to our microbiome, although evidence for correlation exists, evidence for causation is not so clear. Recent work published in the journal Cell has shown that the composition of our microbiome changes as we age. Could this observation be correlation? That our microbiome adapts itself to an aging body, or could this be causal? An indication that changes in your microbiome may alter longevity? And what does this have to do with our genome or epigenome?

Some reports suggest the diet to be a major, controllable, environmental factor influencing the composition of the host microbiome. Professor Tim Spector from King’s College London has dedicated his life to studying identical twins. Originally a geneticist, Prof. Spector is a firm believer that environmental factors are tightly linked to how our genes are expressed, shaping our health and identity. More important are the millions of microbes inside our bodies, which he believes are the key to a happy, healthy and long life. Perhaps alongside focusing on the genetic regulation of healthy aging, we should pay equal attention to prebiotic regulation of longevity.

The question remains, is aging down to genetics or the environment?

At the end of the day, the speed of individual aging will depend on a number of factors, both genetic and environmental. Our genetic code, laid down while we were conceived, is the blueprint of each and every cell in our body. However, this code is susceptible to change, be it through epigenetics, or the interplay with our microbiome, both of which can be influenced by our environment. Taking care of our mental health through relaxation techniques as well as eating diverse, natural foods may be the key to keeping us young and happy!